In fluid machines such as compressors for use, for example, in pipelines and large turbo refrigerators, a fluid introduction portion that introduces a fluid is provided with a suction casing for supplying the fluid from the fluid introduction portion to the apparatus main unit entirely in the circumferential direction about the rotation axis. Such a suction casing includes, for example: a suction nozzle that introduces a fluid from an outer circumferential side to an inner circumferential side in the radial direction; and a circular flow passage formed in a doughnut shape in communication with the suction nozzle. The suction casing has a construction that introduces the fluid in the axial direction through the circular flow passage (for example, see Patent Document 1).
In the fluid machine as described above, a fluid is required to be uniformly supplied entirely in the circumferential direction of the suction casing in order to improve performance and suppress vibration. Therefore, a suction casing as shown in FIG. 7 and FIG. 8 is adopted. Namely, in a compressor 50 as shown in FIG. 7 and FIG. 8, a suction casing 51 includes: a suction nozzle 52; a chamber 53 formed in a doughnut shape in communication with the suction nozzle 52; and a suction flow passage 54 that is formed in a trumpet-like shape on an inner circumferential side of the chamber 53 and opens along an axial direction L in a part of an inner circumferential wall of the chamber 53. In such a suction casing 51, the suction flow passage 54 opens only in a part of the axial direction in the inner wall of the chamber 53. Therefore, a fluid F introduced from the suction nozzle 52, after having been filled in the chamber 53 entirely in the circumferential direction C, flows into the trumpet-shaped suction flow passage 54, and is then introduced to an apparatus main unit 55. As a result, it is possible to make the fluid more uniform in the circumferential direction C compared with the construction as disclosed in Patent Document 1.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2007-309154
However, even with the suction casing 51 shown in FIG. 7 and FIG. 8, some of the fluid F having been introduced from the suction nozzle 52 may flow directly into the suction flow passage 54 without circulating in the circumferential direction C in the chamber 53, and may be supplied to an impeller 55a on the apparatus main unit 55 side. Therefore, to make the fluid F uniform in the circumferential direction, it is required to make the chamber 53 larger in the axial direction, leading to a problem in that the fluid machine as a whole is made larger in the axial direction.
The present invention has been achieved in view of the aforementioned circumstances, and provides a suction casing and a fluid machine capable of introducing a fluid in the axial direction as one uniform in the circumferential direction while they are made smaller in the axial direction.